Safety valve venting system for diphenylamine process



June 28, 1960 G. L. WIESNER SAFETY VALVE VENTING SYSTEM FOR DIPHENYLAMINE PROCESS RIL -NORMAL Mm; LEVEL m TANK Filed Sept. 18, 1956 Him IN V EN TOR.

BY GEORGE L. VHESNER ATTORNEY ican Cyanamid Company, New York, N. a corporation of Maine Filed Sept. 18, 1956, Ser. No. 610,558

1 Claim. (Cl. 260-576) This invention relates to method and apparatus for safety venting in processes in which a liquid chemical is processed under conditions of heat and pressure. More particularly, the invention relates to a venting system in the vapor phase deamination of aniline to diphenylamine, which throughout the specification will be referred to by its industrial abbreviation, DPA.

Processes which are operated at elevated temperatures or high pressures or both require safety valves to prevent explosion of the equipment when undue pressures are developed. In many cases it is feasible to vent the safety valve to the atmosphere usually through a short stack through the roof of the building in which the reaction equipment is housed. If, however, the vapors are dangerous, either because they are inflammable and so constitute a fire hazard or because they are toxic, or both, this method of venting a safety valve is not satisfactory. The loss of product when a safety valve blows may also be substantial. The vapor phase deamination ofaniline to DPA is a typical instance of a chemical reaction such as is described above as the vapors are both inflammable and toxic. Therefore, the invention will be described in greater detail in conjunction with the vapor phase DPA process, although, of course, it will be obvious that what is said is equally applicable to any other chemical reaction which presents the same conditions.

In the vapor phase deamination of aniline to DPA, liquid aniline is maintained in a feed tank which, in conventional plants, is usually a large one, having a capacity of many thousands of gallons. From this tank aniline is pumped through preheaters and superheaters and brought up to a temperature of nearly 500 C. and usually a pressure which'may run from 30 p.s.i. to 150 p.s.i. The hot compressed vapors then pass through tubular converters containing the deamination catalyst, the out gases are condensed and the DPA separated out and the unreacted aniline recycled. Because the conversion to DPA per pass is small, of the order of magnitude of a few percent, there is a very large recirculating load of aniline.

Normally a plant uses several converters in parallel as the catalyst has to be regenerated from time to time. Each converter and superheater require protection by standard safety valves, which are calibrated to relieve at a predetermined pressure. The aniline vapors which are released if a safety valve blows are quite inflammable and are also toxic so that the venting problem is a very serious one. It has been proposed to lead the vents from the safety valves to a high stack. This is extremely expensive and, unless the stack is hundreds of feet high, the problem of a toxicity hazard still remains because under unfavorable weather conditions small concentrations of the vented aniline and DPA vapors may sink to the ground, and aniline is toxic in very low concentrations if inhaled for a considerable period of time. Of course, when a safety valve blows into the stack, all of the aniline and DPA vented is lost, which is an added cost factor.

The present invention avoids any danger from fire or tsd. t s P wn toxicity and, at the same time,prevents any loss of not when asafety valve blows.- The'invention will be described in greater detailin conjunction with the -draw-;

inginwhich;;,; r s, Theiigureis an elevation in diagrammatic system using the present invention,

In the drawing one. of anumber of DPA-converters shown at 1 with a safety valve at 2 venting into a line 3 into which the safety valve from other converters, superheaters, etc., are also led. The aniline feed tank 5 is a large size and is designed so that in normal operation it cannot be emptied. This is effected by locating the aniline feed pumps 6, of which two are shown, with intakes 'well above the bottom of the tank. Cleaning out of the tank can only be effected deliberately under authority of suitable supervisory personnel through a locked valved drain pipe 7. The tank has a short vent stack 8 which'is designed to take care of very small amounts of vapor which may be given off from the aniline at ordinary atmospheric temperatures. The line 3 is led to the bottom of the tank where it terminates in a perforated sparger pipe 4 which functions as a gas diffuser. This pipe is submerged well below the surface in a relatively large volume of aniline. In a tank of commercial size, this minimum capacity may be of the order of 5,000 gallons or even more.

When a safety valve blows, the hot vapors of aniline, DPA and small amounts of ammonia which are generated in the reaction flow through the line 3 into the sparger pipe 4 where they are distributed as fine bubbles into the cold aniline. Hot aniline vapors are immediately condensed and any DPA present is condensed and dissolved, and not lost, as it is pumped again through the cycle and recovered at its normal point. The stack 8 is suflicient to carry the small amounts of ammonia present outside of the building in which the tank is located so that no acute toxicity problem is presented. The ammanio vapors, of course, are lighter than air and so dissipate almost immediately.

Th present invention is applicable to any processes in which a liquid is fed. The only limitations are that the bulk of the gases which would'be expelled through a safety valve are condensible and are not violently chemically reactive with the feed liquid. In cases where two or more liquids are fed into a reaction, the venting can be distributed through the feed tanks or restricted to the one .where the optimum condensing conditions prevail.

I claim:

In combination with a process system for the vapor phase deamination of analine to diphenylamine which includes the steps of introducing liquid aniline into said system as the feed thereto; heating and vaporizing the aniline; in a closed reactor under pressures of from about 30 to about p.s.i., contacting resultant aniline vapor with a deamination catalyst at elevated temperatures, whereby a vapor mixture is produced comprising aniline vapor, diphenylamine vapor and ammonia gas; withdrawing as product a flow of said vapor mixture from said reactor and from the system; and also intermittently discharging additional portions of said vapor mixture from said reactor through a separate safety vent means: the method of treating said intermittently discharged portions which comprises the steps of; (1) establishing in a separate enclosed vessel (a) a volume of liquid phase mixture comprising liquid aniline and (b) thereabove a vapor phase volume of liquid phase mixture at a level below thef --,.Patented- June, 28, 1360 orm of at surface thereof and in the form of fine bubbles, whereby aniline and diphenylamine in the so-discharged vapor mixture is condensed and the condensate remains in said volume of liquid phase mixture and the ammonia in said so-discharged vapor enters said vapor phase mixture thereboth the volume and the temperature of said volume of liquid phase mixture remain substantially constant.

References Cited in the file of this patent UNITED STATES PATENTS 839,319 Rateau Dec. 25, 1906 1,338,698 Richardson May 4, 1920 1,422,494 'Tauberg July 11, 1922 1,749,235 Stafford et a1 Mar. 4, 1930 2,507,132

Woodward May 9, 1950 

